0300 - 0399
0327 - Count of Range Sum (Hard)
Problem Link
https://leetcode.com/problems/count-of-range-sum/
Problem Statement
Given an integer array nums and two integers lower and upper, return the number of range sums that lie in [lower, upper] inclusive.
Range sum S(i, j) is defined as the sum of the elements in nums between indices i and j inclusive, where i <= j.
Example 1:
Input: nums = [-2,5,-1], lower = -2, upper = 2
Output: 3
Explanation: The three ranges are: [0,0], [2,2], and [0,2] and their respective sums are: -2, -1, 2.Example 2:
Input: nums = [0], lower = 0, upper = 0
Output: 1Constraints:
1 <= nums.length <= 10^5-2^31 <= nums[i] <= 2^31 - 1-10^5 <= lower <= upper <= 10^5- The answer is guaranteed to fit in a 32-bit integer.
Approach 1: Ordered Set
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
class Solution {
public:
tree<long long, null_type, less_equal<long long>, rb_tree_tag, tree_order_statistics_node_update> T;
// lower <= sum[j] - sum[i] <= upper
// sum[j] - sum[i] >= lower
// sum[j] - sum[i] <= upper
// where i < j
// given sum[j], find the number of i such that
// 1. i < j
// 2. sum[j] - upper <= sum[i] <= sum[j] - lower
int countRangeSum(vector<int>& nums, int lower, int upper) {
long long sum = 0, ans = 0;
// normalise as lower <= sum[j] - 0 <= upper
T.insert(0);
for (auto x : nums) {
// prefix sum
sum += x;
// count the range
ans += T.order_of_key(sum - lower + 1) - T.order_of_key(sum - upper);
// update T
T.insert(sum);
}
return ans;
}
};0323 - Number of Connected Components in an Undirected Graph (Medium)
Author: @wkw | https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/
0329 - Longest Increasing Path in a Matrix (Hard)
Author: @ColeB2 | https://leetcode.com/problems/longest-increasing-path-in-a-matrix/